1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for cell load sharing within a wireless telecommunications system, and specifically to adapting the threshold for cell load sharing based upon current traffic situations.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as wireless network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Services Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 12 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the wireless network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS 24 is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTSs 24 and 28, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 and 28 components, as a whole, are generally referred to as a Base Station System (BSS) 25. The radio interface between the BTS 24 and the MS 20 utilizes Time Division Multiple Access (TDMA) to transmit information between the BTS 24 and the MS 20, with one TDMA frame per carrier frequency. Each frame consists of eight timeslots or physical channels. Depending upon the kind of information sent, different types of logical channels can be mapped onto the physical channels. For example, speech is sent on the logical channel, "Traffic Channel" (TCH), and signaling information is sent on the logical channel, "Control Channel" (CCH).
With further reference to FIG. 1, the PLMN Service Area or wireless network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the Mobile Stations 20 currently located within the MSC/VLR area 12. If an MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 will request data about that MS 20 from its home HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the home HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.
Many wireless service providers have a feature called Cell Load Sharing (CLS), which is an efficient way to distribute the traffic evenly in the wireless system. Consequently, the radio resources are utilized in an efficient manner, resulting in an increased average capacity (handling ability). The traffic load, e.g., the percentage of available traffic channels in use, in a cell 22 varies over time. In addition, as the traffic load increases in one cell 22, a neighboring cell 27 may have a low traffic load. The CLS feature allows service providers to share the traffic load between the neighboring cells 22 and 27. For simplicity, only one neighboring cell 27 is shown in FIG. 1. However, it should be understood that the number of neighboring cells 27 depends upon the type of cell cluster arrangement within the cellular network 10.
In the current CLS functionality, one threshold defines at what load the traffic load shall be distributed to neighboring cells 27 (BTS's 28) and another threshold determines at what load the traffic from neighboring cells 27 can be accepted. However, these thresholds are fixed, and thus, cannot take into account the dynamic nature of variations on the traffic load in a cellular network 10. Consequently, the CLS feature does not work when an unexpected variation in the traffic load occurs in a cell 22, such as when a high level of traffic occurs due to an automobile accident. For example, as the traffic in one cell 22 due to an unexpected variation increases beyond the threshold for sharing the load with neighboring cells 27, the BSC 23 serving the cell 22 and neighboring cells 27 attempts to perform handovers to neighboring BTS's 28 for those MS's 20 near the border between the cells 22 and 27. However, when the traffic load in the neighboring cells 27 rises above the threshold for accepting load, no handovers can be performed, resulting in a high traffic load in the problem cell 22 with no means of cell load sharing. If, however, the threshold for accepting load in the neighboring cell 27 can be lowered, the load on the problem cell 22 could be reduced. In addition, by raising the threshold for sharing load in the problem cell 22, fewer handovers need to be performed, which results in a more efficient utilization of channel resources.
It is, therefore, an object of the present invention to provide for adaptive thresholds based upon the traffic load to determine cell load sharing between neighboring cells.